This invention relates generally to lens systems, and more particularly to an endoscope objective lens suitable for collecting white light and fluorescence images, where the numerical aperture and entrance pupil diameter is large to allow higher collection power for weak fluorescence signal, while maintaining a small overall diameter.
Conventionally, endoscopes are utilized for places that are difficult to see directly, especially inside human bodies. As its objective lens system, various kinds constituted of multiple lens elements are known.
While conventional retrofocus lens systems for endoscopy cover a large field of view, this type of arrangement usually has a small entrance pupil diameter in order to minimize third order aberrations at large field and thus maintain high optical performance. Although this is normally adequate for bright field imaging, it is not optimized for fluorescence, where the typical fluorescence signal strength is substantially weaker than the white light image. The small entrance pupil means that the collection efficiency of the objective is very weak. It is advantageous for an objective intended for dual modality imaging to have improved collection power, maintain a small overall diameter, large FFOV, easy of manufacturing and high optical resolution for both visible and near infrared wavelength.